1. Field of the Art
The present invention relates in general to a filter device for compressed air, and more particularly to such a filter device for compressed air which is capable of efficiently separating and removing from the compressed air, liquid particles such as water and oil, and solid particles, which are contained in the compressed air.
2. Discussion of the Prior Art
Generally, conduits for supplying compressed air to various pneumatically operated components used in various factories, atomic plants and medical equipment, for example, are provided with a filter device for removing water, oil and solid matters contained in a stream of the compressed air, for the purpose of protecting the pneumatic components or improving the performance of those components.
One type of such a filter device for compressed air is disclosed in U.S. Pat. No. 4,483,618 to David O. Mann, which is constructed as shown in FIG. 6. This filter device includes two kinds of filter means. Namely, the disclosed filter device includes first filter means 10 having a suitable first packing or pad 20 inside a sleeve 18 thereof, and second filter means 12 having a suitable second packing or pad 22 inside another sleeve 18 thereof. The first and second filter means 10, 12 are disposed parallel with each other on an air-tightly enclosed trap chamber 16 having a suitable volume capacity, so as to extend in the vertical direction from the trap chamber 16, such that each of the first and second filter means communicates with the trap chamber 16. The filter device further has a manifold 14 having an inlet conduit 24 and an outlet conduit 26 for compressed air. The manifold 14 is attached to the first and second filter means 10, 12, such that the inlet and outlet conduits 24, 26 communicate with the first and second filter means 10, 12, respectively. According to this arrangement, the compressed air entering the inlet conduit 24 of the manifold 14 is fed through the first filter means 10 into the trap chamber 16, and then through the second filter means 12 into the outlet conduit 26 of the manifold 14, whereby an air passage for the compressed air is formed through the device. In FIG. 6, the reference numeral 28 designates a drain valve, through which liquid separated from the compressed air and accumulated in the trap chamber 16 is discharged out of the filter device.
Usually, the first packing 20 of the first filter means 10 is a wound wire mesh fabric formed of stainless steel fibers or other metallic materials, while the second packing 22 of the second filter means 12 is a wound fabric mesh formed of cotton fibers, for example. As the compressed air passes through the first filter means 10, vapor and/or liquid particles contained in the compressed air are condensed or coalesced, whereby the vapor and/or liquid particles are separated from the compressed air. Subsequently, the compressed air from which the vapor and/or liquid particles have been separated is introduced into the second filter means 12, so that any liquid and solid particles remaining in the compressed air are adsorbed and vaporized by the second filter means 12. Thus, the amount of the vapor and/or liquid and solid particles contained in the compressed air is minimized.
In the above-described filter device, the wound metal wire fibers used as the first packing 20 of the first filter means 10 suffer from some problems as described below. Namely, it is difficult and cumbersome to wind the metal wire fibers, so that the wound metal fibers are dense over the entirety of the first filter means without considerable gaps or voids left therein. Further, the winding condition of the metal fibers as the first packing tends to vary depending on individual workers who produce the first packing, resulting in a clearance between the inner circumferential surface of the filter sleeve and the outer circumferential surface of the wound packing accommodated therein. Therefore, the compressed air passes through the clearance thus formed or through the gaps which inherently exist in the packing, thereby deteriorating the efficiency of removal of the liquid particles contained in the compressed air. Accordingly, the filtering performance of the filter device as described above is likely to fluctuate.
Further, the first packing made of the wound metal fibers as described above is progressively clogged during a long period of use. It is therefore required to regularly replace the clogged wound packing with a new one. However, this regular replacement undesirably increases the maintenance cost of the filter device since the packing is made of a relatively expensive material, such as stainless steel.